The invention relates to a method of checking the quality of a weld bead and to a device for implementing said method.
The invention relates more particularly to a method of checking the quality of a weld bead produced by means of a welding tool, of the type comprising at least the following successive steps:                collection, by means of an optical pyrometer having a high-frequency acquisition sensor, of at least one signal representative of the temperature of a molten portion of the weld bead; and        processing/analysis of said signal for the purpose of identifying possible defects in the weld bead.        
When it is correctly carried out, welding, or the production of a weld bead, is a means widely used in the industry for producing a strong and reliable joint between two workpieces, especially two metal workpieces.
It is essential for the quality of the weld bead to be strictly and rigorously checked so as to ensure a high level of performance and reliability of the joint produced by means of a weld bead.
As is known, the weld bead is checked by visual inspection by an operator, or by optical inspection automatically by profilometric control.
Profilometry is a measurement method that consists in determining the profile of a surface.
Profilometric control is effective, but it is not sufficient for reliably evaluating the quality of a weld bead, as it provides information only about the external appearance of the weld bead.
By analyzing the temperature of the weld bead, more precisely by analyzing the signal representative of the temperature of the molten metal of a portion of the weld bead, it is possible to check the quality of the bead.
The signal representative of the temperature, hereafter called the temperature signal, is analyzed for the purpose of detecting a possible defect in the weld bead, or even of identifying the type of defect generated in question.
Various means are known for measuring the temperature of the molten metal of a weld bead.
A first known means comprises an infrared thermal camera, which delivers an image representative of the temperature of the observed zone, the image being analyzed and processed for the purpose of detecting a possible defect in the weld bead.
One drawback of an infrared thermal camera is its poor processing time/resolution ratio.
This is because either the image collected by the camera has a large number of pixels, in which case the resolution is good but the image processing time is long, or the collected image has a small number of pixels, in which case the processing time is short but the image resolution is too low.
A second known means for collecting the temperature of the molten metal of a weld bead is an optical pyrometer.
An optical pyrometer is a device capable of capturing the thermal radiation emitted by an element by means of a sensor and of delivering a signal representative of the temperature of said element.
Optical pyrometers are not all suitable for measuring the temperature of a weld bead, as some pyrometers deliver a signal having an acquisition frequency below the frequency of the physical phenomena that are encountered during the formation of the weld bead.
In addition, some optical pyrometers are not suitable for the emissivity of certain materials, which falsifies the precision of the measured temperature signal.